1. Field of the Invention
The present invention relates to a method of performing a handoff in a wireless asynchronous transfer mode (ATM) network.
2. Background of the Related Art
Typically, in order to break from the communication service only for voice and to provide a multimedia service of diverse types of traffic communication services, diverse handoff methods are provided to guarantee the mobility of a user in a wireless ATM (WATM) network accompanying a radio network technology and a high-speed network technology.
Especially, in establishing a new communication path, it is required to develop a handoff method that may minimize occupation of network resources in comparison to the existing handoff technique.
Recently, with the appearance of a micro cell and a pico-cell, the radius of the cell becomes still smaller. Accordingly, as shown in FIG. 1, many cells share the same ATM switch to form a cluster.
In the above-described network environment, the cells inside the cluster are divided into crust cells and core cells. The crust cell indicates cells located in a boundary area of the cluster, and the core cell indicates cells whose adjacent cells are all of the crust cells.
Meanwhile, the handoff for guaranteeing the mobility of terminals based on the above-described cells is briefly classified into two kinds. An intra domain handoff is a handoff produced when any terminal moves between the core cells and an inter domain handoff is a handoff produced when any terminal moves between the crust cells.
FIG. 1 is a diagram illustrating a configuration of cells in a WATM network. FIG. 1 shows that one ATM switch is connected to many core cells and crust cells.
FIG. 2 is a diagram illustrating a structure of a conventional WATM network. FIG. 2 shows that each ATM switch is connected to crust cells of each cluster.
FIG. 3 is a diagram illustrating the conventional inter-domain handoff procedure.
Referring to FIG. 3, the term “Path_Setup_Req.” denotes a path setup request message, and “Path_Setup_Ack.” denotes a path setup completion acknowledgement message. Referring to FIG. 3, many request messages should be produced for the path setup, and also many acknowledgement messages are produced in response to the request messages. When a terminal moves between the core cells, the intra handoff is produced inside the one ATM switch. Accordingly, traffic data may be transferred from a service base station (Src_BS) providing the terminal with a radio access service to a newly added base station (New_BSs) without interruption.
On the contrary, when a terminal moves between the crust cells, the inter domain handoff is produced. Unlike the intra handoff, the inter domain handoff does not share the one ATM switch, a delay until a communication path is established between base stations of the crust cellscluster may be produced, and this may cause the deterioration of the communication quality due to data loss.
In order to overcome the above disadvantages, the inter domain handoff estimates the moving path of the terminal, and sets the communication path by preoccupying a communication resources for a neighboring ATM switch. Accordingly, the inter domain handoff may support the non-interrupted handoff like the intra domain handoff.
The conventional inter domain handoff technique estimates the moving path of the terminal, and preoccupies available resources of all the base stations. The preoccupied resources are required for the non-interrupted handoff, but causes waste of the communication resources.
Also, when the terminal moves along the boundary region of the cluster, the number of kinds of the communication resources is increased due to the frequent occurrence of the inter domain handoff Further, the number of messages produced for establishing the communication path is rapidly increased, and this causes the network load.